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Vernon Owens works at Jugtown Pottery, Seagrove, North Carolina.
I. Building The Kiln
SITE The first thing to consider when building a groundhog kiln is water drainage. It should be possible to get drainage away from kiln in all directions. If you have a hillside it will make a lot less work in getting the hole ready to start the kiln, starting the front at the foot of the hill and digging back into it. This way part of the chimney will be underground. Level ground works just as well as far as the kiln is concerned (keeping drainage in mind). If you build the kiln on top of the ground brace the sides with iron posts, then fill in the stacking chamber with dirt up to the level you want the floor.
SHELTER Kiln shelter ought to be at least 3' wider than kiln on each side. If kiln is built where ground freezes deep, chimney should also be sheltered. Build the shelter 10-12' past front of kiln for storing wood and working space.
SIZE AND MA TERIALS We have built several different types and sizes and have found large kilns too hard to heat to high stoneware temperatures. In firing earthenware you can use a longer kiln and do your bisque in the back. Since a groundhog kiln is fired from one end it will always get hotter at the front. This is a problem in salt-glazing because you may get pots too hot in the front and not hot enough at the back. In burning glazed pots these kilns work good because you can use a lower melting glaze at the back. I think a good size kiln is 12' long, including the firebox which is 4' long and 5' wide. A good smaller size would be 4' x 10' with a 3' firebox. Since you don't use shelves in these kilns it should be built as low as possible. A 22" center from flint stone is a good height. With a 12" wall this gives a 10" arch rise. (Don't get atraid of getting in and out — I am six' tall and I can do it.)
DRAFT: GRATE, FAN Since these kilns have nothing but natural draft it is a good idea to put some kind of grate for the wood to burn on. The grate has to be either cast iron or fire clay brick or large blocks. I think the large blocks are called "car-tops" made to go in tunnel kilns. You would need to get this material second-hand if possible. It is expensive new and don't last long for a grate. Another way to keep the draft going good is to put in a small (squirrel cage) fan and pipe air under the grate. Not too much air as this will blow too many ashes back on the pots. Keeping a good draft is the main thing for a good firing.
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